Dengue fever is a natural focal infection caused by arboviruses of the same name and occurring with a flu–like syndrome or hemorrhagic manifestations. Classical dengue fever is characterized by a two–wave rise in temperature, myalgia, arthralgia, lymphadenitis, exanthema, hemorrhagic – spontaneous bleeding. Epidemiological and clinical data, the results of virological and serological analyses are taken into account when diagnosing dengue fever. Specific therapy and immunization have not been developed, so the treatment is mainly symptomatic.
Dengue fever (bone–breaking disease, joint fever) is a transmissible viral infection occurring in two clinical forms – classical and hemorrhagic. Disease is common in regions with tropical and subtropical climates: Southeast Asia, South America, Australia and Oceania, the Mediterranean basin, etc. Hundreds of thousands of cases are registered annually in endemic foci. There are imported cases of dengue fever outside the area of infection, due to both the migration of infected persons and the import of infected mosquitoes. The classical form has a benign course, but the hemorrhagic form is characterized by high mortality.
Dengue virus refers to arboviruses of antigenic group B belonging to the genus Flavivirus, family Togaviridae. There are 4 pathogen serovars (DEN-1, DEN-2, DEN-3, DEN-4), each of which is capable of causing both the classical and hemorrhagic form. After infection with one or another serotype of the virus, lifelong type-specific immunity remains, but this does not exclude the possibility of infection with another serotype of the virus in the future. Dengue-virus has a single-stranded RNA, a two-layer lipid envelope, a virion diameter of 40-45 nm. By its antigenic structure, the dengue virus is close to the viruses of yellow fever, West Nile and Japanese mosquito encephalitis. The dengue virus is resistant to freezing and drying, but is labile to the effects of heating, ultraviolet light, and proteolytic enzymes.
Reservoirs and sources of infection are sick people, monkeys, bats, and carriers of the virus are mosquitoes of the genus Aedes (A. albopictus and A. Aegypti, A. Polinesiensis, A. Cutellaris). Mosquitoes become contagious on 8-12 days after blood sucking and retain a lifelong ability to transmit the virus. Healthy people become infected with dengue fever through the bites of infected mosquitoes. To a greater extent, children under 2 years of age, elderly and weakened people, as well as visitors, including tourists, are susceptible to dengue fever. Local residents of endemic areas and visitors get sick mainly with classical dengue fever. Children who have previously had classical dengue caused by type 1, 3 or 4 viruses are more likely to become infected with severe hemorrhagic dengue fever when infected with the second type of virus.
After a mosquito bite, the virus multiplies in regional lymph nodes and vascular endothelium for 3-5 days. After the period of primary replication, viral particles enter the bloodstream, causing the development of viremia, which is clinically manifested by fever-intoxication syndrome. The second wave of fever is associated with the penetration of viruses into organs and tissues. Relief of clinical symptoms occurs as viral neutralizing and complement-binding antibodies accumulate in the blood. In the hemorrhagic form of dengue fever, damage occurs mainly to small vessels, a violation of the aggregate state of the blood with the development of multiple hemorrhages in the membranes of the heart, pleura, gastrointestinal mucosa, brain.
Dengue fever can occur in two clinical variants: classical and hemorrhagic (without shock syndrome or with dengue shock syndrome). After the incubation period (from 3 to 15 days after the mosquito bite), a short-term prodromal period occurs, during which malaise, headache, signs of rhinitis and conjunctivitis are noted. Sometimes acute manifestations occur against the background of complete well-being without previous symptoms.
In the classical form of dengue fever, chills develop, a rapid increase in body temperature to 39-41 ° C. During this period, patients experience nausea, anorexia, arthralgia, ossalgia and myalgia, which hinder movement. Typical objective signs are bradycardia, lymphadenitis, hyperemia of the pharynx, injection of sclera vessels. After 3-4 days, the body temperature drops sharply, and a short period of apyrexia lasting 1-3 days occurs. Then a second wave of fever develops, accompanied by the same symptoms.
A typical sign of classic dengue fever is an exanthema that appears during the first or second fever wave. The rash is polymorphic, more often – bark–like, sometimes – urticary, scarlet-like or petechial. Skin rashes are abundant, localized on the trunk and extremities, accompanied by itching and peeling of the skin. The total duration of the acute period of classical dengue fever is 7-9 days. The period of convalescence stretches for 4-8 weeks, during which asthenia, insomnia, joint and muscle pain persist.
Hemorrhagic form of dengue fever, also known as Philippine, Singapore, Thai hemorrhagic fever, has a more severe course. In the initial period, as well as in the classical form, there is an increase in temperature and intoxication. Joint and muscle pain is rare, but severe abdominal pain and liver enlargement are characteristic. On 2-3 days, a petechial rash appears on the skin, in severe cases spontaneous nasal, gingival, uterine, gastrointestinal bleeding, hemorrhages into internal organs, hematuria develop. On 3-5 days from the onset of fever, dengue shock syndrome may develop, accompanied by tachycardia, arterial hypotension, oligoanuria, DIC syndrome, cyanosis and convulsions.
To determine the severity of clinical manifestations and to assess the prognosis, 4 degrees of hemorrhagic dengue fever are distinguished:
- I: clinical signs – feverish intoxication syndrome and a “positive tourniquet test”; laboratory – thrombocytopenia and hemoconcentration.
- II: clinical signs (additionally) – bleeding (ecchymosis, from the nose, gums, genital tract, bloody vomiting, melena); laboratory signs – an increase in thrombocytopenia and hemoconcentration.
- III: clinically – signs of circulatory insufficiency, development of dengue shock; laboratory – increased thrombocytopenia and hemoconcentration.
- IV: deep shock syndrome of dengue.
In hemorrhagic dengue fever, deaths are recorded in 5-20% of cases, mainly among children. The surviving patients may have complications in the form of polyneuritis, pneumonia, encephalitis, meningitis, mumps, otitis media, orchitis, thrombophlebitis, etc.
Diagnosis and treatment
The criteria developed by WHO make it possible to suspect dengue fever in the event of the development of: febrile syndrome lasting 2-7 days; thrombohemorrhagic syndrome; thrombocytopenia (less than 100×109/L) and an increase in Ht by 20%; hepatomegaly and shock syndrome. The presence of epidemiological prerequisites (visits to endemic regions, mosquito bites, outbreaks of infection) and typical clinical symptoms (two-wave fever, arthralgia, myalgia, exanthema) are also taken into account. An additional criterion may be a positive “tourniquet test” (intradermal hemorrhage after applying a tourniquet or cuff in the area of the elbow bend).
Laboratory confirmation of dengue fever is carried out by isolating the virus from the patient’s blood by PCR and determining the increase in the titer of specific antibodies in paired sera in dynamics using RSC, RNIF, PH, RTGA. Dengue fever should be differentiated from pappatachi and chikungunya fever, yellow fever, malaria, meningococcal infection, sepsis; in children – from measles, scarlet fever, rubella.
Etiotropic therapy of dengue fever is absent, therefore, therapeutic measures are mainly symptomatic (taking antipyretics, antihistamines, detoxification). In the hemorrhagic form, hemostatic and antishock therapy, correction of DIC syndrome, transfusion of erythrocyte and platelet mass, blood plasma are performed. There is evidence of the effectiveness of parenteral administration of interferon in the early stages of the disease.
Prognosis and prevention
The classic form of dengue fever usually proceeds favorably and ends with recovery. With hemorrhagic form, the prognosis is serious, largely depending on the patient’s age, the serotype of the virus, and the timing of the start of therapy. The highest mortality rate is observed among young children.
Experimental vaccines against dengue fever are currently at different stages of clinical trials, so we can only talk about non-specific prevention. To prevent infection in regions endemic to the development of dengue fever, it is necessary to use repellents and fumigators that repel mosquitoes, mosquito nets. Of particular relevance is the destruction of mosquitoes carrying the dengue virus, the use of insecticides, the fight against swampiness and littering of the territory, the storage of water reserves in closed containers.Disease is a natural focal infection caused by arboviruses of the same name and occurring with a flu–like syndrome or hemorrhagic manifestations. Classical form is characterized by a two–wave rise in temperature, myalgia, arthralgia, lymphadenitis, exanthema, hemorrhagic – spontaneous bleeding. Epidemiological and clinical data, the results of virological and serological analyses are taken into account when diagnosing dengue fever. Specific therapy and immunization have not been developed, so the treatment of dengue fever is mainly symptomatic.